In April of 2004, I bought a 256MB SD card for, as I recall, around $120. This is a cost of $480/GB.
Today I bought an 8GB SD card for $40, or $5/GB.
That means that in the ensuing 54 months, the cost of the technology has been cut in half nearly 7 times. The technology has doubled in cost density every 8 months or so—it's been good couple of years for flash memory.
It's also hit "double the space for half the cost" once every 15 months.
Of course, all of these numbers hinge a small bit on how well I remember how much I paid for that first 256MB card.
SD card storage - another reason to love Canon.
Everybody is on board the SD bus at this point besides Sony and Olympus.
I actually don't mind the Memory Stick format all that much since many peripherals support it—for instance, my X's Drive will take CF, SD, or MS.
But xD is right out. I had to skip Olympus cameras entirely because of that.
--D